The existing pressure sensitive ink jet media for various commercial ink jet printers and inks, such as sold by Apple, Hewlett Packard, Canon, Epson and the like, work under the mechanism in which the ink absorption relies principally or partially on the absorption of the ink into voids of substrate fiber and/or silica gel pigment particles, and/or heavy coating thickness. It dries slowly. The print feathers, bleeds, and has low color saturation and poor resolution. The print smears readily, smudges easily, and requires immediate interleaving. The print also has a high water sensitivity and will be washed off upon contact with water such as under outdoor display conditions where it is subject to rain.
The current market does not offer waterproof aluminum foil/plastic film self-adhesive ink jet media. Due to the fact that these substrates are absolutely non-porous, non-absorbing, non-penetrating to ink jet inks, normal approaches are to increase the coating thickness (e.g., 17 g/m2), using significant loading of porous micro-absorbing white pigment (e.g., silica to resin=63.37), which result in opaqueness and poor resolution.
The present composition for forming an ink jet receptive coating to a base substrate overcomes the aforesaid problems of the prior art.
The present invention provides a water proof ink jet ink-receiving media with a pressure sensitive adhesive (PSA) applied to the back side for sticking to a receiving surface. While it comprises several coating layers applied to conventional substrate (as will be made more clear in FIG. 1), principal inventiveness resides in the composition of pressure sensitive ink jet receptive media. Its component elements provide a medium of excellent receptivity to ink jet printing and generate photorealistic output. The printed ink is fast drying (within a minute). The resulting image has a high resolution, relatively high gloss and exhibits bright, vivid and saturated color gamut. The printed image is free of feathering and bleeding and is resistant to abrasion and scratching as well as being water proof and outdoor weatherproof.
The ink jet receptive coating (top coating) of the present invention comprises the following components:
(1) Binder
The binder""function is to bond pigment particles to one another and to the surface of the plastic or foil substrate stock. The binder determines the viscosity of the coating mix and its drying characteristics. The binder has a great deal to do with the ink acceptance (hence the printability), the smoothing or calendaring properties, water and oil resistance, and the pick strength and foldability of the coated substrate.
(2) Charge Control Agent
Conductive polymers are selected to interact with the dye molecules on the ink receptive layer. Hydrophilic cationic homo-polymers or co-polymers having positive charges that are capable of electrically absorbing negatively charged ink jet ink ions are used. The positive charge carried by the conductive polymer attracts the anionic dye ions in the ink and thus functions to localize and fix the dye.
(3) Cross-Linking Agent
Inorganic and organic compounds capable of reacting with the primary polymer matrix by forming chemical or hydrogen bonds with its hydroxyl, carboxyl, NH or other functional groups to form a strong linkage are employed. They serve to increase melting point, reduce swelling after immersion in water, waterproof the network and provide abrasion, scratch and smudge/scuff resistance.
The composition can be self-crosslinking where it has hydroxyl functional groups; or other cross-linking agents such as epoxy, formaldehyde, or glyoxal can be incorporated.
(4) Adhesion Enhancing Agent
Gelatin, alpha-olefin such as polyethylene polypropylene, polyethylene acrylic acid and poly-acrylic acid may be incorporated in the present composition.
(5) Dispersant
Surfactant or wetting agents are employed to reduce the surface tension of the substrate so that the normal coating can be uniformly spread without streaking or other undesirable coating defects. Examples of surfactants include anionic polymers (polyacrylic, lignosulfonate, naphthalene sulfonate), alkali silicates, nonionic polymers (fatty alcohols, ethylene oxide), and various fluorinated surfactants.
(6) Porous Ink-Absorptive Pigment
Such pigments may optionally be present where a non-glossy product is desired. In such cases, various fine-grained, micro-porous, negatively or positively charged pigments such as silica gels are preferred.
The relative proportions of elements in the compositions of the present invention are set forth in Table 1 below with all percentages being on weight basis.
The present ink jet receptive coating particularly resolves the difficulty of using non-permeable, non-porous, non-penetrating substrates which are non-absorptive to ink jet inks, such as polyester, styrene, vinyl, polypropylene films, aluminum foil, or metalized plain or holographic plastic films coated on the other side with pressure sensitive substrates. The resulting product is a digital printing medium which is pressure sensitive, self adhesive, and easy to apply.
The coating of the present invention specifically provides electrical attraction to ink jet ink and maximizes its absorption to the specific substrates utilized. The balance of the composition of the ink-receptive coating attracts and fixes ink. The polymers being utilized exhibit hydrophilic properties and are electrically positive charged and thus have the ability to absorb water and negatively charged ink. The polymers contribute excellent physical properties to the product. They have hydroxyl and/or carboxyl functional groups and can be either self-cross-linked or cross-linked by the addition of epoxy or other hardening agents to obtain necessary water-resistance and anti-abrasion properties.